The invention relates to an automatic exposure control circuit for photomicrographic apparatus.
When observing a specimen on a microscope, it is often desirable to take a picture of the specimen being observed at any desired time, which can be effected by means of a photomicrographic apparatus, i.e. a microscope with photographic apparatus. An automatic exposure control circuit for such apparatus is responsive to a light from the specimen, which light is split into an observation optical system and a photographic optical system by means of a path splitting prism. The light in the photographic optical system is introduced into the photographic apparatus, and is further split by another path splitting prism into a viewer path and an exposure path also. The light in the latter path impinges upon a photoelectric transducer element contained in the automatic exposure control circuit. After a shutter is released, the automatic exposure control circuit operates to provide a porper exposure to a photosensitive film.
The automatic exposure control circuit of the kind described essentially comprises an electronic shutter circuit. Unlike a conventional photographic camera, the photographic apparatus associated with a microscope is not provided with an exposure diaphragm, so that the only exposure controlling factors are film speed and shutter speed. Because of the relationship between the brightness of a light source and that of an object being photographed, the shutter speed in an automatic exposure operation is limited to a speed value corresponding to an exposure period less than 1/100 second, and a higher shutter speed in excess of 1/100 second can not be used because of the above relationship and the restrictions imposed by a shutter mechanism. In view of this, it is desirable in the photographic apparatus associated with a microscope that for a relatively long exposure period in excess of 1/100 second in an automatic exposure operation, some means be used to display that the electronic shutter is in operation. In a conventional apparatus, the electronic shutter circuit is utilized for this purpose to illuminate a lamp while the electronic shutter is in operation, thus indicating that the specimen is being photographed.
However, before the electronic shuter is operated, it is necessary to determine whether the automatic exposure is feasible for a specimen being photographed. If a favorable exposure condition prevails between the brightness of the specimen being photographed and that of the light source, the electronic shutter will be operated with a shutter speed less than 1/100 second, initiating an automatic exposure to assure a satisfactory photograph. If an automatic exposure is attempted without regard to the above mentioned relationship, a good picture can not be taken. In particular when taking a color picture, the color temperature of the light from the light source which irradiates the object being photographed, namely, the specimen, is also involved. Thus, in order to assure an optimum exposure in an automatic manner by the operation of the automatic exposure control circuit, there is a need to display by some means whether or not an automatic exposure is possible for a particular specimen being photographed, before the shutter is released.
When releasing a shutter, a manual operation of the release member may inadvertently shift the body of the microscope. As an alternative, the use of an electromagnetic plunger is contemplated to urge the release member, but as is well known, the force from the electromagnetic plunger increases in an accelerated manner, so that the release may result in applying oscillations to the body of the microscope. Therefore, it is essential that the release member be operated in a quiet and smooth manner by remote controlling means.